Yup, Strangers in Prax. I have the module. That addition was, if I recall correctly, pretty much a DM fiat. I don't recall there being any benefit to the PCs for helping Barran do his thing other than standard physical rewards. So good on your GM! I certainly thought that helping someone accomplish what Barran does should have had more impact on the PCs (and thought it was lame they couldn't accompany him to the Hero Plane).
(Of course I could be wrong, its been awhile since I looked at that module so I may have forgotten or missed it).
Edit: I was wrong. You can get 'gifts' while inside the Vomiter by doing certain things, so yeah, good spot! Thanks for that.